The present invention relates to a disc drive assembly. In particular, the present invention relates to an improved suspension design for supporting a head relative to a disc surface.
Disc drive systems are known which read data from a disc surface during operation of a disc drive. Such disc drive systems include conventional magnetic disc drives and optical disc drive systems. Optical disc drive systems operate by focusing a laser beam onto a disc surface via an optical assembly which is used to read data from the disc surface. Discs are rotated for operation of the disc drive via a spindle motor to position discs for reading data from or writing data to selected positions on the disc surface.
Known optical assemblies include an objective lens and a solid immersion lens (SIL) which is positioned between the objective lens and the disc surface. The SIL is positioned very close to the data surface of the disc and is described in U.S. Pat. No. 5,125,750 to C. Orle et al., which issued Jun. 30, 1992, and in U.S. Pat. No. 5,497,359 to Mamin et al., which issued Mar. 5, 1996. In these optical systems, a laser beam is focused onto the SIL using an objective lens. The SIL is preferably carried on a slider and the slider is positioned close to the disc surface. Use of an SIL increases storage density.
The slider is generally formed of a transparent material and includes an air bearing surface to fly the SIL above the disc surface. The slider includes a leading edge and a trailing edge. Rotation of discs creates a hydrodynamic lifting force under the leading edge of the slider to lift the leading edge of the slider to fly above the disc surface in a known manner. The slider preferably flies with a positive pitch angle in which the leading edge of the slider flies at a greater distance from the disc surface than the trailing edge.
The slider and SIL are supported above the disc surface via a suspension assembly which includes a load beam and gimbal spring 36. The slider is coupled to the load beam via the gimbal spring. The load beam applies a load force to the slider via a load button. The load button defines an axis about which the slider pitches and rolls via the gimbal spring. The slider is preferably resilient in the pitch and roll direction to enable the slider to follow the topography of the disc. Preferably, it is desired that the gimbal spring be rigid in the in-plane direction for retaining precise in-plane slider positioning.
The flexure of the gimbal spring permit the air bearing slider to pitch and roll as the slider flies above the disc surface. It is important to maintain the proximity of the SIL and slider relative to the disc surface to maintain the proper focus of light to the disc surface as is known for optical disc drive systems. It is important that the flexure system including the load beam and the gimbal spring be designed to stably and accurately support the SIL during operation of the disc drive system. Also in a magneto-optic (M-O) system, a magnetic transducer element is carried on the slider to write data to the disc surface. It is also important to accurately support and position the magnetic transducer elements relative to the disc surface during operation of the M-O system.
An actuator mechanism is coupled to the suspension assembly to locate the SIL relative to selected disc positions for operation of the disc system. During movement of the suspension system, force is transmitted through the load beam and gimbal spring to move the slider. Operation of the actuator mechanism, air bearing surface, and spindle motor introduce external vibration to the slider and suspension assembly. Depending upon the mass and stiffness of the suspension assembly, including the gimbal spring and load beam, external vibration may excite the load beam and gimbal spring at a resonant frequency, thus the input motion or external vibration may be amplified substantially, thus causing unstable fly characteristics and misalignment of the slider relative to the disc surface.
External vibration or excitation of the suspension assembly and slider may introduce varied motion to the slider and suspension assembly. Depending upon the nature and frequency of the excitation force, the slider and suspension assembly may cause torsional mode resonance, sway mode resonance, and bending mode resonance. Torsional mode motion relates to rotation or twisting of the suspension assembly about an in-plane axis. Bending mode resonance essentially relates to up/down motion of the suspension assembly relative to the disc surface. Sway mode vibration relates to in-plane lateral motion and twisting. It is important to limit resonance motion to assure stable fly characteristics for the SIL. In particular, it is important to control the torsion and sway mode resonance, since they produce a transverse motion of the slider, causing head misalignment.
The resonance frequency of the suspension assembly for torsion and sway mode resonance is related to the stiffness or elasticity and mass of the suspension system. Thus, it is desirable to design a suspension system which limits the effect of sway mode and torsion mode resonance in the operating frequencies of the disc drive while providing a suspension design which permits the slider to pitch and roll relative to the load button which has relatively high lateral rigidity and stiffness for maintaining precise in-plane positioning of the slider along the yaw axis.